Robust, efficient, and broadband SHG of ultrashort pulses in composite crystals

We experimentally demonstrate efficient second-harmonic generation (SHG) of tunable ultrashort pulses of 100 femtoseconds, using a novel method based on composite segmented periodically poled (CSPP) design. The scheme was borrowed from the nuclear magnetic resonance (NMR) composite pulses (CP) of Shaka and Pines. Using CSPP, a broadband and efficient conversion over a bandwidth of 35 nm in very short interaction length was achieved. In addition, CSPP showed robustness to temperature changes up to 90°C. Two CSPP schemes with 15 and 31 segments and periodically poled design were implemented on Mg-doped LiNbO₃ crystal. The CSPP performance was shown to be superior in all aspects. The experimental results are compared to numerical simulation with excellent agreement.